Whole Muscle and Single Motor Unit Twitch Profiles in a Healthy Adult Cohort Assessed With Phase Contrast Motor Unit MRI (PC-MUMRI)

Abstract

Background: Motor units (MUs) control the contraction of muscles and degenerate with age. It is therefore of interest to measure whole muscle and MU twitch profiles in aging skeletal muscle. Purpose: Apply phase contrast MU MRI (PC-MUMRI) in a cohort of healthy adults to measure whole anterior compartment, individual muscles, and single MU twitch profiles in the calf. Assess the effect of age and sex on contraction and relaxation times. Study Type: Prospective cross-sectional study. Subjects: Sixty-one healthy participants (N = 32 male; age 55 ± 16 years [range: 26–82]). Field Strength/Sequences: 3 T, velocity encoded gradient echo and single shot spin echo pulsed gradient spin echo, echo-planar imaging. Assessment: Anterior shin compartment (N = 47), individual muscle (tibialis anterior, extensor digitorum longus, peroneus longus; N = 47) and single MU (N = 34) twitch profiles were extracted from the data to calculate contraction and relaxation times. Statistical Tests: Multivariable linear regression to investigate relationships between age, sex and contraction and relaxation times of the whole anterior compartment. Pearson correlation to investigate relationships between age and contraction and relaxation times of individual muscles and single MUs. A P value <0.05 was considered statistically significant. Results: Age and sex predicted significantly increased contraction and relaxation time for the anterior compartment. Females had significantly longer contraction times than males (females 86 ± 8 msec, males 80 ± 9 msec). Relaxation times were longer, not significant (females 204 ± 36 msec, males 188 ± 34 msec, P = 0.151). Contraction and relaxation times of single MUs showed no change with age (P = 0.462, P = 0.534, respectively). Date Conclusion: Older participants had significantly longer contraction and relaxation times of the whole anterior compartment compared to younger participants. Females had longer contraction and relaxation times than males, significant for contraction time. Evidence Level: 2. Technical Efficacy: Stage 1.